147 



produced, being a little longer than the anterior, and is acumi- 

 % nate behind. The dorsal margins are straight and very sloping, 

 especially the posterior, which is a little longer than the an- 

 terior ; the ventral margin is regularly curved. 



Dimensions. — A.ntero - posterior, So ; and umbo - ventral 

 diameters, 2*75 millimetres. 



Locality. — Lower beds at Muddy Creek. 



FAMILY UNGULINID.E. 



Diplodonta subquadrata, spec. nov. Plate xiv., figs. 10a— 106. 



Shell quadrately-orbicula.r, moderate^ convex, thin, trans- 

 lucent, inequilateral, equivalve ; posterior side broad, with a 

 subtruncated margin, anterior side narrower and rounded. 

 The ornament consists of rather coarse concentric lines of 

 growth, with here and there broader ones. Umbones small, 

 antemedian, acute. 



Dimensions of an average size specimen : — Antero-posterior 

 diameter, 13 ; umbo-ventral diameter, 11*5 ; sectional diameter, 

 9 millimetres. 



Localities. — Muddy Creek (lower beds) ; oyster-beds of the 

 Eiver Murray Cliffs at Nor'-AVest Bend'; Table Cape, Tas- 

 mania (JR. M. Johnston!) 



The nearest ally of this species is D. Tasmanica, T. "Woods, 

 from which it differs by its more quadrate outline and regular 

 sculpture, and in being less inequilateral ; it closely resembles, 

 also, D. Zealandica, Gray, which is more inflated, and has a 

 rounded ventral margin. 



Sacchia suborbicularis, spec. nov. Plate xviii., figs. 10a- 10c. 



Shell triangularly orbicular, depressed, rather solid ; pos- 

 terior side rounded, somewhat produced anteriorly. Umbones 

 small, obtuse, produced, approximate ; lunule obsolete, margins 

 of valves simple. Surface marked with distant growth-folds, 

 smooth at the umbones. 



The left valve has two divergent cardinal teeth ; the anterior 

 one is stout and triangular, the posterior one is thin and elon- 

 gate, behind which is a broad and deep triangular cartilage 

 groove. In the right valve there are two cardinal teeth sepa- 

 rated by a triangular pit, which receives the strong anterior 

 tooth of the left; the anterior tooth is confluent with the 

 dorsal edge, but the posterior is elongate, narrowly triangular, 

 grooved on the face, and free from the dorsal edge ; there is a 

 cartilage groove corresponding with that in the left valve. No 

 lateral teeth. Pallial line entire. 



Dimensions. — Antero-posterior diameter, 7*5 ; umbo-ventral 

 diameter, 8 ; sectional diameter, 3*75 millimetres. 



